1. Field of the Invention
The present invention relates to a method of forming a color diffusion transfer image by heat development. More particularly, the invention relates to a method capable of producing a sharp color image by diffusion transfer of an image formed in a thermally developed photographic material.
2. Description of the Prior Art
Conventionally, color images are formed with a photo-sensitive material (silver halide) by using a dye formed by the interaction of two components, i.e. the oxidation product of a color developing agent and a color coupler, or by the silver dye bleaching method wherein the image is formed by bleaching the dye with silver, or by the color diffusion transfer process used in instant color photography wherein the dye is diffused and transferred in an alkaline processing solution. Either of these methods requires a water-soluble processing solution and involves complicated image-forming procedures. Therefore, a novel heat development process that is dry and requires simple procedures to form a color image has long been desired.
Conventional methods of forming color images by heat development are described in Japanese Pat. No. 7782/69, U.S. Pat. Nos. 3,761,200 and 3,764,328, and Japanese Patent Applications (OPI) Nos. 27132/81 and 27133/81 (the symbol OPI as used herein means an unexamined published Japanese patent application). These methods depend on the interaction between the oxidation product of a color developing agent and a color coupler. However, in these methods, the silver image is formed in the area where the dye image is formed, so either color smearing by the silver image or staining of the background due to printout after development is unavoidable. To eliminate these problems, desilvering and fixing steps are necessary, but then, the simplicity and dryness of the heat development process are impaired.
Another type of method of forming a color image by heat development is the silver dye bleaching method described in Japanese Patent Applications (OPI) Nos. 105821/77, 105822/77, 50328/81, and U.S. Pat. No. 4,235,957. However, in order to bleach the dye image, an activated sheet containing a strong acid and a silver halide complexing agent is necessary, and this leads to complicated procedures and requires very careful handling of the strong acid.
Still another type of method of forming a color image by heat development is the diffusion transfer process that is described in Japanese Patent Applications (OPI) Nos. 179840/82 and 186744/82. This is an interesting approach that eliminates the defects of the first two methods, but on the other hand, the image formed by this method is low in archival quality and lightfastness, and its archival quality cannot be improved without sacrificing transferability.